The present invention relates generally to optical fiber intrusion systems, and more particularly to providing local area warning of optical fiber intrusion.
Recent years have seen a proliferation of telecommunication services. With the additional services has come an increased need for network infrastructure, including in particular, buried cables and associated equipment. One type of cable is fiber optic cable, which generally contains multiple optical fibers bundled together within one cable.
Fiber optic cable is subject to damage, especially when buried close to the surface or when located in the vicinity of a construction site. Since a single fiber optic cable may carry a very large amount of data, the failure of a single fiber optic cable may result in service outage for a large number of customers. As such, network service providers take precautions in order to avoid such failure.
One technique for monitoring buried fiber optic cable is disclosed in U.S. Pat. No. 5,778,114, entitled Fiber Analysis Method and Apparatus. That patent describes a fiber intrusion detection system for detecting an intrusion or potential intrusion to a buried fiber optic cable. That system includes an optical splitter for splitting an optical signal into sub-signals for injection into opposite ends of a looped optical fiber. The signals emanating from the opposite fiber ends are recombined at the splitter for receipt at a detector that measures the phase difference between the optical sub-signals. A processor compares the phase difference measured by the detector to known phase difference measurements associated with different types of threats. By matching the actual phase difference to the known phase difference measurement associated with a particular type of intrusion, the processor can thus identify the nature of the intrusion.
While detecting the fiber intrusion threat is important, in order to avoid actual damage to a fiber optic cable, it is also important to warn the potential intruder of the imminent threat. However, an alarm at a central network location may not allow for network provider personnel to reach the actual threat location (e.g., construction site) in time to avoid the damage. In recognition of this problem, the '114 patent discloses a disturbance monitor that may be dispersed along the right-of-way of the fiber optic cable for providing a visible and/or audible warning in the field in response to a signal from the fiber intrusion detection system. The '114 patent discloses a wireless link between the fiber intrusion detection system and the disturbance monitor for signaling an alarm condition. One disadvantage of that configuration is that a wireless communication link may not always be available, or such a link may provide an unreliable communication channel.